A thermoplastic elastomer composition, formed by a dynamically heat treating of a rubber and an olefinic resin in the presence of a crosslinking agent, does not require a vulcanizing step and can be easily formed into a molded article by an ordinary molding method for a thermoplastic resin, such as injection molding, profile extrusion molding, calendering or blow molding.
However, such dynamically crosslinked olefinic thermoplastic elastomer is inferior in elastic recovering property to a vulcanized rubber. For improving such elastic recovering property, there have been investigated an increase in the crosslinking density and a higher Mooney viscosity in the rubber. These methods improve the elastic recovery but the thermoplastic elastomer composition loses fluidity significantly. Also in order to improve the moldability, there can be employed a method of adding a peroxide-decomposable olefinic rubber, but such method is associated with a drawback that the elastic recovering property is deteriorated. It has thus not been easy, in the prior technologies, to obtain a thermoplastic elastomer composition in which the elastic recovery and the moldability are well balanced.
Also in recent years, thermoplastic elastomers which are a rubber-like soft material not requiring a vulcanizing process and having a moldability similar to that of thermoplastic resins are attracting attention and used in various fields such as automotive parts, parts for consumer electric appliances, parts for medical and food instruments, electric wires, and household goods. In such thermoplastic elastomers, those of polyolefin type, polystyrene type, polyurethane type, polyester type, polyvinyl chloride type or the like. have been developed and commercialized. Among these, particularly useful are a blend employing an olefinic resin and an ethylene•α-olefine random copolymer rubber as principal raw materials, and an olefinic dynamically crosslinked thermoplastic elastomer employing an olefinic resin and an ethylene•α-olefine random copolymer rubber as principal raw materials and partially crosslinked with a crosslinking agent. These materials have excellent heat resistance, weather resistance, cold resistance and moldability, and are relatively inexpensive. For these reasons, these materials are attracting attention, particularly in automotive parts or the like, as a replacement of metal parts for the purpose of a weight reduction, a replacement for RIM urethane parts for the purposes of an improvement in the service life of the parts and for a cost reduction, a replacement for vulcanized rubber for the purposes of simplification of working process, recyclability and a cost reduction and a replacement for soft polyvinyl chloride for the purpose of an improvement in the service life and an improvement in contamination, and consumption of these materials is increasing year after year.
However the olefinic dynamically crosslinked thermoplastic elastomer is inferior in a surface scratch resistance (scratch resistance), and is still insufficient for use in molded articles requiring scratch resistance, such as an inner panel or a surface material of a console box.
Also the olefinic dynamically crosslinked thermoplastic elastomer is excellent in heat resistance, ozone resistance and weather resistance, also has a rubber elasticity similar to that of vulcanized rubber, and also has a moldability almost comparable to olefinic thermoplastic resins such as polyethylene or polypropylene. Utilizing these properties, it is employed in molded products requiring rubber elasticity such as a bumper, an external lace, a window sealing gasket, a door sealing gasket, a trunk sealing gasket, a roof siderail, an emblem, an internal surface finishing material or the like. for an automobile. It is also employed in various gaskets for construction use. Among these, the olefinic dynamically crosslinked thermoplastic elastomer used in the applications particularly requiring rubber elasticity such as automotive gaskets for window sealing, door sealing, trunk sealing or the like, and gaskets for construction purpose can be obtained by increasing the content of the ethylene•α-olefine copolymer rubber component in comparison with the olefinic dynamically crosslinked thermoplastic elastomer employed in other applications.
However, the olefinic dynamically crosslinked thermoplastic elastomer obtained in this manner has a low fluidity at the molding, and it is difficult to directly produce an automotive gasket or a construction gasket of a complex shape by injection molding. On the other hand, a prior process for molding such gaskets is complex and requires a long work time as explained in the following, and an improvement is strongly desired for work saving and for improving productivity.
For molding a gasket, for example in case of ordinary vulcanized rubber, there has been employed a process of forming a linear portion of the gasket by a profile extrusion molding of unvulcanized rubber, then vulcanizing the article produced by profile extrusion molding, and adding and vulcanizing a curved adjoining portion between ends of such molded articles in slit molds thereby forming a connecting part. However, such process requires the vulcanizing step twice. In order to simplify such process and reduce the work time, there are conceived a method of replacing the adjoining portion between the ends of the profile extruded and vulcanized articles by an olefinic dynamically crosslinked thermoplastic elastomer not requiring vulcanization and a method of replacing also the profile extruded articles of the linear portions with an olefinic dynamically crosslinked thermoplastic elastomer, and the former method is considered desirable practically. In such method of replacing the adjoining portion between the ends of the profile extruded and vulcanized articles by the olefinic dynamically crosslinked thermoplastic elastomer, there is adopted a method of placing profile extruded articles in a split mold and injecting an olefinic dynamically crosslinked thermoplastic elastomer in an adjoining portion thereby fusing the end portions. However, in most cases, it is difficult to obtain a fusion with a practically acceptable adhesion strength. For example, JP-B-61-53933 proposes a method, in mutually adjoining extrusion molded articles of an olefinic dynamically crosslinked thermoplastic elastomer, of preheating the articles to be adjoined thereby improving the adhesion strength. Also JP-A-59-221347 proposes a method, in a similar adjoining, of employing an olefinic dynamically crosslinked thermoplastic elastomer containing crystalline poly-1-butene thereby improving the adhesion strength even without preheating. However, in these methods, a sufficient effect cannot be obtained particularly in case the member to be adjoined is olefinic vulcanized rubber. Consequently there is strongly desired a development of an olefinic composition thermoplastic elastomer composition showing an excellent injection fusibility for an olefinic vulcanized rubber and an olefinic dynamically crosslinked thermoplastic elastomer as the material to be adjoined.
Furthermore, the olefinic dynamically crosslinked thermoplastic elastomer, having a flexibility and excellent rubber-like properties and not requiring a vulcanizing step, can produce a molded article by a molding method for ordinary thermoplastic resins such as injection molding, profile extrusion molding, calendering, or blow molding. For this reason, it is recently used increasingly, in view of energy saving, resource saving and recyclability, in automotive parts, industrial products, electric and electronic parts, construction materials or the like. as a replacement for vulcanized rubber or vinyl chloride resin.
However, in automotive parts such as a glass run channel or a window lace, it is associated with drawbacks of a low slidability to a window pane and a low durability.
For improving the slidability, JP-A-2000-26668 discloses an olefinic thermoplastic elastomer composition prepared by adding organopolysiloxane and an aliphatic amide to an olefinic dynamically crosslinked thermoplastic elastomer. Also JP-A-2000-143884 discloses an olefinic thermoplastic elastomer composition formed by adding acryl-denatured organopolysiloxane and a higher fatty acid or a higher fatty acid amide to an olefinic dynamically crosslinked thermoplastic elastomer or employing these in combination.
However, either composition shows an insufficient slidability, and also has a drawback that the appearance becomes defective because of bleeding out of aliphatic acid amide.
Furthermore, JP-A-2000-959000 discloses an olefinic thermoplastic elastomer formed by adding organopolysiloxane of a viscosity of 10 cSt or higher but less than 106 cSt, organopolysiloxane of a viscosity of 106 to 108 cSt and a fluorinated polymer to an olefinic dynamically crosslinked thermoplastic elastomer.
However, though a high content of organopolysiloxane provides a satisfactory slidability, organopolysiloxane showing a low mutual solubility with the olefinic dynamically crosslinked thermoplastic elastomer causes bleeding out, thereby providing an unpleasant sticky feeling when the surface is touched, and there is strongly desired the development of an olefinic dynamically crosslinked thermoplastic elastomer free from bleeding-out phenomenon and showing excellent slidability.